Threshold drains are used on balconies, and general outdoor areas such as patios and entertainment areas. Threshold drains enable the formed areas outside a building to be made substantially level with the floor levels inside the building. Such an equality of levels ensures safe passage of wheelchairs, traymobiles and other wheeled implements, and invalids and other persons who require the assistance of a walking cane.
A threshold drain also dramatically reduces the risk of surface water penetrating a building via a door threshold, and also collects run-off from doors and windows during storms. The Building Code of New Zealand provides a standard set out in Clause E2 External Moisture which requires that a gap extend between the building wall and the grate of the adjacent threshold drain. Other countries or jurisdictions have equivalent or similar standards.
Hitherto the construction of the threshold drain has required two concrete pours. The first pour forms the drain trench or gutter. Thereafter the support frame for the grate of the drain is installed on the poured concrete. Next a second concrete pour takes place so as to cover the supporting arms of the support frame and build up the exterior concrete surface to the level of the interior floor (less any provision for subsequent pavers to be laid on the exterior concrete surface).